The Ecological Risk Assessment Support Center (ERASC) recently completed an external review draft of the document titled, "Application of Equilibrium Partitioning Theory to Soil PAH Contamination". It addresses the issue of whether equilibrium partitioning techniques can be used to predict the toxicity of PAH mixtures in soil. This was announced in the May 23rd Federal Register Notice.

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In March 2004, ORD's Ecological Risk Assessment Support Center (ERASC) received a request from the Ecological Risk Assessment Forum (ERAF) to provide insight into the issue of whether equilibrium partitioning (EqP) techniques can be used to predict the toxicity of polycyclic aromatic hydrocarbon (PAH) mixtures in field-collected soil. EqP theory, which was developed for sediments, assumes that toxicity to sediment organisms is directly proportional to the amount of unbound contaminant - in this case PAH - dissolved in sediment porewater. Therefore, if one can predict how much of the bulk sediment PAH is bound to the organic carbon on sediment particles (and, therefore, by difference calculate how much is in the porewater), then toxicity prediction can be done solely on the basis of LC50s (or, alternatively, Water Quality Criteria) derived from water-only studies.

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